undef the methods as late as possible and scope it to the object only

lib/graphql/client/schema/object_type.rb

@@ -19,6 +19,7 @@ def self.new(type, fields = {})
 
             const_set(:READERS, {})
             const_set(:PREDICATES, {})
+            const_set(:METHODS_TO_UNDEF, [])
           end
         end
 
@@ -62,8 +63,8 @@ def initialize(klass, defined_fields, definition, spreads)
               @klass::READERS[:"#{name}"] ||= attr
               @klass::PREDICATES[:"#{name}?"] ||= attr
 
-              @klass.undef_method(name) if BASE_RUBY_METHODS.include?(name) && @klass.method_defined?(name)
-              @klass.undef_method("#{name}?") if BASE_RUBY_METHODS.include?("#{name}?") && @klass.method_defined?("#{name}?")
+              @klass::METHODS_TO_UNDEF << name if BASE_RUBY_METHODS.include?(name)
+              @klass::METHODS_TO_UNDEF << "#{name}?" if BASE_RUBY_METHODS.include?("#{name}?")
             end
           end
 
@@ -190,6 +191,12 @@ def initialize(data = {}, errors = Errors.new, definer = nil)
 
           @definer = definer
           @enforce_collocated_callers = source_definition && source_definition.client.enforce_collocated_callers
+
+          self.class::METHODS_TO_UNDEF.each do |method_name|
+            begin
+              singleton_class.undef_method(method_name)
+            rescue; end
+          end
         end
 
         # Public: Returns the raw response data

test/test_client.rb

@@ -856,6 +856,11 @@ def method
       def equal
         "equal"
       end
+
+      field :test, String, null: false
+      def test
+        "test"
+      end
     end
 
     schema = Class.new(GraphQL::Schema) do
@@ -864,12 +869,14 @@ def equal
 
     @client = ::GraphQL::Client.new(schema: schema, execute: schema)
 
-    Temp.const_set :Query, @client.parse("{ method things equal }")
+    Temp.const_set :Query, @client.parse("{ method things equal test }")
 
     result = @client.query(Temp::Query)
+
     assert_equal "method", result.data.method
     assert_equal "things", result.data.things
     assert_equal "equal", result.data.equal
     assert_predicate result.data, :equal?
+    assert_equal "test", result.data.test
   end
 end